It will be time to go short when everyone except a few weirdos agrees that the market is going up, and those few weirdos receive comments like "ok....whatever" or "I may not be as smart as you in trading, but why would I trade contra to the trend of the last two years ?" or "This is annoying and immature." Once you see a thread like that here on ET, you will still have to wait until posting to it stops for about a month or two, and then you can start shorting the market.